A problem in this field sometimes relates to the stability of the rachidian implants in the discal space once they have been implanted. This stability may aide intervertebral disc prostheses to preserve a certain degree of mobility to the vertebrae between which they are implanted, but also may aide other types of implants, for example when arthrodesis is desired, for example by using intersomatic cages and/or other implants allowing arthrodesis (which may for example be achieved by means of auxiliary stabilizing structures such as osteosynthesis bars. Indeed, for example, there can exist a risk that the implant moves in the intervertebral space under the effect of the forces experienced during movement of the patient, even when the implant is provided with catches or teeth on its vertebral contact surfaces. It is therefore often desirable to attach the rachidian implant to the adjacent vertebrae between which it is implanted. In the case of arthrodesis, provision is also often made for osteosynthesis bars immobilizing the vertebrae, for example with lordosis, in order to avoid the possibility that the cage moves out of the intervertebral space. In the prior art, solutions are known which provide the rachidian implant with a bone anchoring device which allows the implant to be firmly fixed in the vertebrae between which the implant is intended to be implanted.
Another problem in the field sometimes relates to invasivity and access to the intervertebral spaces (discal spaces) which is often delicate because of congestion, notably because of the presence of blood vessels and nerves in the vicinity of the intervertebral space, as well as the proximity of the spinal cord. The bone anchoring devices which have to penetrate sufficiently deep into the vertebrae in order to ensure proper attachment, therefore may benefit from a small size while allowing the implant to be attached without jeopardizing the blood vessels and the surrounding nerve tissues (for example by not requiring more room in the vicinity of the intervertebral space than required for the implantation of the actual rachidian implant). For example, certain implants (notably intersomatic cages) are equipped for being implanted through a posterior route (from the rear of the patient) or a transforaminal route (through the foramen). The posterior route generally requires partial resection of the articular joints and passes between the dura mater and the articular joints (generally two cages positioned substantially parallel to the sagittal plane are provided). This route therefore often follows a direction very close to the spinal cord and uses cages of reduced dimensions. The transforaminal route follows an oblique route with regard to the sagittal plane and requires cages of reduced dimensions but of sufficient length so as to be positioned obliquely or perpendicular to the sagittal plane. Generally, small access routes are sought for limiting the invasivity of the surgical implantation operation. Further, with this view of limiting invasivity, it is optionally sought to avoid having to lay additional equipment (either posterior or anterior), such as osteosynthesis bars (with pedicle screws generally) or osteosynthesis plates. The use of anchoring means for attaching the cages might give the possibility of addressing this problem if these anchoring means are reliable. The cages are generally placed between the vertebrae at an anterior position on the vertebral plates, so as to impose a lordosis. The osteosynthesis bars may be used for imposing lordosis which prevents the cage from moving backwards but anchoring means therefore may be preferred over them if the obtained attachment and stability of the implant are reliable. Such anchoring means therefore preferably limit invasivity as well, in addition to being reliable and stable.
Another problem that may exist for the bone anchoring means relates to ablation. Indeed, it is generally desired to be able to remove the bone anchoring means (and the implant in general). Therefore the bone anchoring means preferably may be retained in the implant in a stable way but they may also be removed as easily as possible. Further, easy ablation should also preferably be feasible with limited invasivity.
In the prior art, notably from the published patent applications WO 2008/149223 and WO2011/080535 filed by the applicant of the present application, to which the reader may refer for examining various problems addressed and the advantages provided by this type of solution, an anchoring device is known, suitable for being firmly implanted and sufficiently deep in the vertebral plate for ensuring good support of the implants applied against these vertebrae, but along an approach axis for insertion, substantially (i.e. generally) in the plane of the intervertebral space. This type of solution typically includes at least one anchor formed by a plate, which is often curved and generally stiff, laid out for penetrating into a plate of a vertebra through an implant and provided with at least one abutment for retaining an implant against this vertebra. This type of anchoring devices or anchor, including a plate intended to be planted into the bone may sometimes pose a risk of the vertebra being split by the plate, during its impaction in the vertebra or under the effect of the forces exerted on the implant and/or on the anchor once it is planted into the vertebra. Also, this type of anchor may sometimes have the risk of causing a too large notch during its impaction in the vertebra, which may induce the possibility of undesirable play of the anchor which risks weakening the (fragile) attachment of the implant and/or making it not very reliable. Application WO2011/080535 is directed to this type of problem, among others. It will be noted that by the term of impaction is meant here the fact of planting the anchoring device into the vertebrae. It will be noted that the present application discloses an impactor which is an impaction device since it is laid out for allowing an anchoring device to be planted in a vertebra. On the other hand, another potential problem of this type of anchor including a plate relates to stiffness. Under certain circumstances, it is important that the anchor be sufficiently stiff so as not to deform and/or not have too much play under the effect of the forces which are exerted thereon, in order to avoid it gradually moving out of the vertebra in which it is anchored and to limit the risk of mobility of the cage in the intervertebral space. The stiffness of this type of anchor is therefore often an important feature for allowing efficient attachment, which in some circumstances may be more efficient than staples or other fine and/or relatively flexible or even fragile devices.
Another problem may relate to the risks of making the implant fragile by the layout of attachment means against the vertebrae. This problem may relate to the size of the anchor relative to the implant, for example the size of the passage of the implant intended to receive this anchor. Indeed, the passing of the anchor through the implant and the maintaining of the stability of this kind of anchor in the implant (possibly subject to a desired play, for example a minimum play) is also an aspect which may facilitate more reliable attachment under certain circumstances. Application WO2011/080535, among other subject matter, also addresses this type of stability problem. These anchoring devices may provide a good anchoring solution with limited invasivity, but they may in some circumstances still require too large a size for adapting to the dimensional constraints of certain implants, such as for example the posterior or transforaminal approach cages, and may therefore be improved for further limiting invasivity. Further, the removal of this type of bone anchoring means may be a problem, for example if it is intended that removal should be easy while limiting invasivity. Also, application WO2013/124453, filed by the applicant of the present application, among other subjects addresses these issues of weakening of the implants by the anchors and of easy removal of the anchors. However, it is still useful to propose other types of solutions, for example addressing these problems in ways that may be more efficient under some circumstances. Further, depending on the relevant type of implant, it may be useful that the generally stiff anchor be retained by a structure which is also firm, in order to minimize damaging the implant under the action of the forces exerted on the anchor and the implant. For example, in the case of an implant of a more flexible or less robust material than that of the anchors, there may exist a risk of weakening the implant or of retaining the anchor in the implant.
In this context, it is interesting to propose solutions that may mitigate one or more of the drawbacks (and/or other ones) of the prior art.